Weather strips and opening trims for automobiles are long stripe-shaped interior parts having sealing ability that are provided in outer frames at doors and bodies in order to keep out rainwater and external atmosphere and to shut out noises.
The aforementioned interior part comprises a body portion (1) having a core (2) with a U-shaped cross-section and surrounding covering layer (3), and a hollow sealing portion (11) formed integrally with the body portion (1).
For this interior part, a metallic core was conventionally used in order to increase fit-holding force with the car body panel. However, recently, from the aspect of productivity and reduction of weight, resin products instead of metals were used as a core, as described in Japanese Patent Application Laid-Open No. 2005-132343. When a metallic core is used, a covering layer is formed by extrusion molding around the plate-shaped core and then the core is bent to form a U-shaped cross-section. Meanwhile, when the core is made of a resin, a U-shaped core can be formed by extrusion molding and a covering layer is subsequently formed by extrusion so that a bending process is not needed, as described in Japanese Patent Application Laid-Open No. 2005-306344.
On the other hand, the covering layer and the hollow sealing portion are generally made of rubbers, as described in Japanese Patent Application Laid-Open No. 2005-132343. Rubber products require a vulcanization process after molded. Since the covering layer and the hollow sealing portion have different functions, the required physical properties are different. In particular, the hollow sealing portion works as cushion, softer rubber than those used for the covering layer is generally used. A softening agent such as oil is added in order to impart pliability to the rubber. However, when a softening agent is used, bleeding may occur which results in deterioration of the appearance. Therefore, a foamed vulcanized rubber is generally used for the hollow sealing portion. It is difficult to form and adhere a non-foamed body portion and a foamed hollow sealing portion together in a single process. Conventionally, a process for forming a body portion by extrusion molding a covering layer over the core and a process of forming a hollow sealing portion by extrusion molding were separately performed, and then the body portion and the hollow sealing portion were bonded together.
Because of the recent increasing concern in environmental issues, there has been a demand to use recyclable thermoplastic elastomers for the rubber covering layer and hollow sealing portions.